Multi-channel (or “wide area”) communication systems provide wide-area coverage for users (also referred to herein as “subscribers”) of the communication system. These communication systems generally comprise a number of radio frequency sites (RF site) corresponding to different general geographic coverage areas defined by a frequency range of one or more infrastructure devices. The infrastructure and corresponding infrastructure devices support and manage one or more communication channels in the coverage area. Accordingly, for purposes of the teachings herein, an RF site includes the infrastructure that serves a particular coverage area with one or more channels for wireless communication device transmissions. Some or all of the infrastructure devices in a multi-channel communication system may be networked or connected together via a backend network to provide wide-area coverage via one or more wide-area channels, and in many instances two or more of the coverage areas and thus, channels, have some degree of overlap.
Multi-channel communication systems may be designed as trunked systems or conventional systems. In trunked systems, a limited number of communication channels are shared among a much larger number of subscribers to facilitate efficient use of the system's communication resources. Thus, to afford each subscriber a reasonable opportunity to use the system's resources, one or more control channels are utilized by the infrastructure to allocate and switch the shared resources between the many subscribers in the system. In general, when a subscriber wants to communicate on the trunked system, he or she sends a request via a wireless communication unit (hereinafter referred to as a “subscriber unit”) on a control channel to communicate with another subscriber or group of subscribers (also referred to herein as a “talkgroup”) on their subscriber units. In turn, the requesting subscriber unit (and the subscriber units to which it attempts to communicate) receives back on the control channel the allocation of a channel to use for communicating. When the communication is concluded, the allocated channel is released for use by other subscriber units in the system.
In conventional systems, on the other hand, a number of communication channels are also shared amongst a number of subscribers (although the number of subscribers per channel is typically much smaller than in trunked systems). There is no control or switching mechanism, however, provisioned in the infrastructure to allocate the resources among the subscribers in the system. Thus, in contrast to a trunked system, each channel in a conventional system is dedicated to one or more talkgroups. The subscriber members of each assigned talkgroup control access to the channel through their subscriber units by manually selecting the channel or selecting the talkgroup that is assigned to the channel in order to start a communication session and transmit and receive media during the session. Currently, narrowband subscriber units are commonly configured for group communications with members of a known group, also known as a talkgroup, simply with the press of a button. Public safety systems enjoy the use of the talkgroup capability of the narrowband subscriber units.
Conventional channels are typically provisioned in the subscriber unit and selected by the user of the subscriber unit through a knob or menu, etc. If a subscriber unit is intended to operate in the coverage area of multiple conventional channels (particularly for wide-area conventional operation), the user needs to know what conventional channel coverage area he is in, and manually switch to the appropriate channel for that coverage area. However, in wide-area conventional systems, the user may not even know, and the subscriber unit may not be configured with channels for, the coverage area of the wide-area system.
In a trunking system, a full-time control channel allows infrastructure control of channel assignments and transmission of adjacent control channel information. This does not solve the problem for most conventional systems, however, because of the cost of the infrastructure, and the system loading required to take advantage of a full-time control channel.
Alternatively, vote scan systems program subscriber units with a number of frequencies, and allow the subscriber units to use any of the frequencies. The subscriber unit scans these frequencies looking for a transmission. The disadvantage of this approach is that a preamble is necessary on every infrastructure transmission to allow time for the scanning subscriber units to scan to the transmit channel and detect the transmission, increasing channel access time.
Accordingly, what is needed is a method for selecting a channel for group communications in a conventional multi-channel communication system.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of various embodiments and elements. In addition, the description and drawings do not necessarily require the order illustrated. It will be further appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required.
Apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the various embodiments so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. Thus, it will be appreciated that for simplicity and clarity of illustration, common and well-understood elements that are useful or necessary in a commercially feasible embodiment may not be depicted in order to facilitate a less obstructed view of these various embodiments.